This invention relates to high purity substantially defect-free alloy sputtering target materials and more particularly, to rare earth-transition metal (RE-TM) sputtering targets useful for producing magnetooptical media, and a method for preparing them.
Conventionally, RE-TM sputtering targets are made by melting the component metals together in an inert atmosphere, for example in the crucible of an induction furnace. The melt is then poured from the crucible into a mold where it is cooled quickly to form an ingot. However, the presence of significant residual stresses in rapidly cooled castings and the brittle nature of RE-TM alloys make it difficult to prepare targets from such materials which are devoid of cracks, voids and other defects.
Generally, defects are minimized and yields are improved in conventional casting processes by maintaining the fluidity of the melt in the mold for an appreciable length of time before casting. However, superheating the melt to improve its fluidity before pouring will alter the alloy composition because of the high vapour pressure of the rare earth metals.
It is therefore an object of this invention to provide high purity substantially defect-free sputtering target materials and a method for making them which is devoid of the foregoing disadvantages.